welcome to the forum.
I believe there is 2 or 3 GB of content. (
groove clips/midi files/rex files, audio files)
https://www.cakewalk.com/Documentation?product=SONAR&language=3&help=Tutorial2.2.htmljust make sure you go to CCC and double check you downloaded all of the loop content.
are you seriously comparing sonar to Acid Pro 7 ?

your getting a DAW that's 10X times better than acid.
loop content can also be found free on line.
the loop content in sonar was never meant to be a selling point, it was placed there to get you started.
and 2 GB of content was plenty for me, I know everyone is different but 2 GB's is enough to get started.
like I said there is plenty of free content to be had on line and hopefully as time goes on you will find yourself making your own loops. that is something you will take great pride in knowing your using your own library's.
its really easy to do as well.
insert a synth, create a part / freeze it/slice it, drag and drop it (it wont be acidized though)
if you want to do that you'll need to read up on groove clip looping
basically sonars version of acidized files
groove clips=acid loops